A primary task of the heart is to pump oxygenated, nutrient-rich blood throughout the body. Electrical impulses generated by a portion of the heart regulate the pumping cycle. When the electrical impulses follow a regular and consistent pattern, the heart functions normally and the pumping of blood is optimized. When the electrical impulses of the heart are disrupted (i.e., cardiac arrhythmia), this pattern of electrical impulses becomes chaotic or overly rapid, and a sudden cardiac arrest may take place, which inhibits the circulation of blood. As a result, the brain and other critical organs are deprived of nutrients and oxygen. A person experiencing sudden cardiac arrest may suddenly lose consciousness and die shortly thereafter if left untreated.
The most successful therapy for sudden cardiac arrest is prompt and appropriate defibrillation. A defibrillator uses electrical shocks to restore the proper functioning of the heart. A crucial component of the success or failure of defibrillation, however, is time. Ideally, a victim should be defibrillated immediately upon suffering a sudden cardiac arrest, as the victim's chances of survival dwindle rapidly for every minute without treatment.
There are a wide variety of defibrillators. For example, implantable cardioverter-defibrillators (ICD) involve surgically implanting wire coils and a generator device within a person. ICDs are typically for people at high risk for a cardiac arrhythmia. When a cardiac arrhythmia is detected, a current is automatically passed through the heart of the user with little or no intervention by a third party.
Another, more common type of defibrillator is the automated external defibrillator (AED). Rather than being implanted, the AED is an external device used by a third party to resuscitate a person who has suffered from sudden cardiac arrest. FIG. 10 illustrates a conventional AED 800, which includes a base unit 802 and two pads 804. Sometimes paddles with handles are used instead of the pads 804. The pads 804 are connected to the base unit 802 using electrical cables 806.
A typical protocol for using the AED 800 is as follows. Initially, the person who has suffered from sudden cardiac arrest is placed on the floor. Clothing is removed to reveal the person's chest 808. The pads 804 are applied to appropriate locations on the chest 808, as illustrated in FIG. 10. The electrical system within the base unit 802 generates a high voltage between the two pads 804, which delivers an electrical shock to the person. Ideally, the shock restores a normal cardiac rhythm. In some cases, multiple shocks are required.
Another type of defibrillator is a Wearable Cardioverter Defibrillator (WCD). Rather than a device being implanted into a person at-risk from Sudden Cardiac Arrest, or being used by a bystander once a person has already collapsed from experiencing a Sudden Cardiac Arrest, the WCD is an external device worn by an at-risk person which continuously monitors their heart rhythm to identify the occurrence of an arrhythmia, to correctly identify the type of arrhythmia involved and then to automatically apply the therapeutic action required for the type of arrhythmia identified, whether the therapeutic action is cardioversion or defibrillation. These devices are most frequently used for patients who have been identified as potentially requiring an ICD and to effectively protect them during the two to six month medical evaluation period before a final decision is made and they are officially cleared for, or denied, an ICD.
The current varieties of defibrillators available on the market today, whether Implantable Cardioverter Defibrillators (ICDs) or Automatic External Defibrillators (AEDs) or any other variety such as Wearable Cardioverter Defibrillators (WCDs), predominantly utilize either a monophasic waveform or a biphasic waveform for the therapeutic defibrillation high-energy pulse. Each manufacturer of defibrillators, for commercial reasons, has their own unique and slightly different take on waveform design for their devices' pulses. Multiple clinical studies over the last couple of decades have indicated that use of a biphasic waveform has greater therapeutic value than a monophasic waveform does to a patient requiring defibrillation therapy and that biphasic waveforms are efficacious at lower levels of energy delivery than monophasic waveforms.
All of the current products that use a biphasic waveform pulse have a single high-energy reservoir, which, while simple and convenient, results in severe limitation on the range of viable pulse shapes that can be delivered. Specifically, the second or Negative phase of the Biphasic waveform is currently characterized by a lower amplitude starting point than the first or Positive phase of the Biphasic waveform, as shown in FIG. 3. This is due to the partial draining of the high-energy reservoir during delivery of the initial Positive phase and then, after inverting the polarity of the waveform so that the Negative phase is able to be delivered, there is only the same partially drained amount of energy remaining in the energy reservoir. This lower amplitude starting point constrains and causes the lower initial amplitude of the Negative phase of the waveform. The typical exponential decay discharge is shown by the Positive phase of the waveform shown in FIG. 5 and how the reservoir would have continued to discharge (if the polarity had not been switched) is shown as a dashed line in FIG. 5.